I opened a cabinet for editing, one in which there is one drawer. In the drawer editor, I've set the drawer box slide mount spec with no product code selected, but my hole pattern is selected. I modified the hole pattern for a Blum 230 550mm slide by creating a new one with only three holes, and then overwriting the pattern file with its many-hole array. The cabinet built fine and has three holes for the slide mount.

Trying out things, in the drawerbox editing mode, I clicked the pattern (my pattern with three holes) and selected instead, the standard out of box Thermwood-created pattern for a Blum 230 that is shorter than the 550mm one. This newly-specified hole pattern has many more than three holes.

Nothing changed in the cabinet. It still has the 3 holes as placed by my original spec, made at drawer-creation time.

Make sure you are clicking the icon at the top to apply the new pattern to the cabinet. If you are doing this as a test, all good, but if you have a lot of cabinets, I highly suggest using Global Item Modification to do it for you.

Go to Cabinet Editor. In the Item Window on the right(where you would normally pick a cabinet), there is a blue box for Adj. Features. Select it, then Global Item Modification at the top. In the lower left corner of the dialog is a blue question mark. Select it and read through the help section about the Global Item Modification. It details about what to do on the first page, and scrolling down further in the help document, there is information about using the applied hardware tab.